Polyurethane elastomers having improved green strength and demold time, and polyoxyalkylene polyols suitable for their preparation

ABSTRACT

Elastomers exhibiting decreased demold times and improved green strength are prepared by reacting a di- or polyisocyanate with a monodisperse polyoxypropylene diol having ultra-low unsaturation, and preferably prepared by the double metal cyanide.t-butyl alcohol catalyzed polymerization of propylene oxide. Further improved demold times and elevated elastomer physical properties are made possible bythe use of multidisperse polyoxyalkylene polyether polyol blends having an overall unsaturation of less than 0.010 meq/g and a polydispersity of about 1.4 or greater.

This is a division of application Ser. No. 08/491,007, filed Jun. 15,1995, now U.S. Pat. No. 5,670,601.

TECHNICAL FIELD

The present invention pertains to polyurethane elastomers displayingimproved green strength and lowered demold times. More particularly, thepresent invention pertains to such elastomers prepared from ultra-lowunsaturation polyoxyalkylene polyols preferably prepared by polymerizingpropylene oxide in the presence of double metal cyanide.t-butylalcohol(DMC.TBA) complex catalysts. The polyurethane elastomers exhibitdramatically improved green strength and diminished demold times ascompared with otherwise similar elastomers prepared from polyols havinglow unsaturation, without diminishing ultimate physical properties ofthe elastomer. The present invention further pertains to uniqueultra-low unsaturation polyoxypropylene polyol blends having broadmolecular weight distribution or polydispersity which further reducedemold time and increase green strength of elastomers preparedtherefrom.

BACKGROUND ART

Processing characteristics are critical in assessing the commercialviability of polyurethane elastomers. Examples of these processingcharacteristics are the pot life, gel time, demold time, and greenstrength, among others. A commercially useful pot life is necessary toenable sufficient working time to mix and degas where necessary, thereactive polyurethane forming components. Gel time is critical inenabling complete filling of molds before gelation occurs, particularlywhen large, complex molds are utilized, while demold time is importantin maximizing part production. Too long a demold time necessitateslarger numbers of relatively expensive molds for a given part output.Demold time is especially critical for glycol extended elastomers whichtend to be slow curing. These requirements are often competing. Forexample, a decrease in catalyst level will generally result in longerpot life and increased gel time, but will often render demold timeunsatisfactory, and vice versa.

Green strength is also important. Green strength is a partiallysubjective measure of the durability of a polyurethane part immediatelyfollowing demold. The characteristics of the polyurethane formingreaction is such that full strength of the polyurethane part does notdevelop for a considerable time after casting. The partially cured, or"green" part must nevertheless be demolded within a reasonable time.Polyurethane parts typically display two types of "poor" green strength.One type is such that the part is gelled and rigid, but is brittle andeasily torn. Those normally skilled in the art of polyurethaneelastomers refer to this type of poor green strength as "cheesy" inreference to its "cheese-like" consistency. The other type of "poor"green strength is when the part is soft and pliable, and permanentlydistorts during the demolding process. By contrast, parts which upondemold display durability and which can be twisted or bent withoutpermanent damage are said to possess "excellent" green strength. Whiledemold time limits production, poor green strength increases scrap rate.

Various methods of increasing green strength and decreasing demold timehave been examined. Increasing catalyst level, for example, may oftendesirably influence these properties. However, as previously stated,increased catalyst levels also decrease both pot life and gel time.Moreover, when microcellular elastomers are to be produced, somecatalysts increase the isocyanate/water reaction to a greater degreethan the isocyanate/polyol reaction, and thus can affect processability.

It is well known in the art that polyurea and polyurethane/ureaelastomers are much easier to process than all urethane elastomers.Polyurea and polyurethane/urea elastomers are prepared usingamine-terminated polyols and/or diamine chain extenders. The most commonurethane/urea elastomer system uses a toluene diisocyanate prepolymerreacted with the diamine extender, methylene-bis-(2-chloroaniline),better known as MOCA or MBOCA. This system is known to give a long potlife (10 to 20 minutes) with commercially acceptable demold times ofless than 60 minutes with excellent green strength. In addition to this,there is minimal sensitivity to changes in processing conditions withthis system. However, some of the physical properties of the elastomerscontaining urea linkages are inferior compared to all urethaneelastomers (i.e. softness, tear strength, resilience and hydrolysisresistance). Other common diamine chain extenders may unduly affect potlife and gel time, however.

Primary hydroxyl-containing polyols have also been used to decreasedemold time and improve green strength with some success, particularlyin RIM applications. However, in general, reliance on high primaryhydroxyl polyols causes a decrease in pot life and gel time andmoreover, may make the elastomers more subject to adsorption of waterdue to the more hydrophilic nature of the polyoxyethylene cap whichprovides the primary hydroxyl content. Elastomers based on primaryhydroxyl polyols are also generally harder than those prepared frompolyoxypropylene homopolymer polyols.

In U.S. Pat. No. 5,106,874 is disclosed the use of polyoxyethylenecapped polyoxypropylene polyether polyols in diamine extendedpolyurethane/urea elastomers where the polyol is prepared using alkalimetal catalysts and low temperatures to minimize polyol unsaturation.The U.S. Pat. No. '874 patentees indicate that when ethylene oxidecapped polyols having an unsaturation of 0.04 meq/g polyol are used inthe preparation of diamine extended elastomers, demold time and greenstrength improve. However, the systems disclosed are rigidpolyurethane/urea elastomers with a high proportion of urea linkagesonly suitable for RIM, as demold times are on the order of 30-40seconds.

Polyol unsaturation and its effect on polyurethane properties has beencommented upon at great length, although the effects are unpredictableand difficult to quantify. The relationship of unsaturation toprocessing has not been studied to any great degree. During synthesis ofpolyoxypropylene polyols by base catalyzed oxypropylation of a suitablepolyhydric initiator, a competing rearrangement produces monohydricallyloxy species which are in turn oxypropylated. The mechanism ofunsaturation formation has been discussed, for example, in Block andGraft Polymerization, Vol. 2, Ceresa, Ed., John Wiley & Sons, pp. 17-21.Whatever the source of terminal unsaturation, it is well known that themol percent of terminally unsaturated monol increases rapidly withincreasing molecular weight of the polyhydric species. Thus, while verylow molecular weight, conventionally catalyzed, polyoxypropylene glycolsof 200 Da to 500 Da equivalent weight may have low monol content, forexample less than about 1 mol percent, a similarly prepared diol of 2000equivalent weight may contain 45 mol percent to 50 mol percent of monol.This large increase in monol content lowers the nominal functionality oftwo to an average functionality of c.a. 1.6 or less.

Polyol unsaturation is generally measured by titration in accordancewith ASTM test method D-2849-69 or its equivalent, and is expressed inmilliequivalents of unsaturation per gram of polyol, hereinafter,"meq/g". Traditional, base-catalyzed polyols in the moderate to higherequivalent weight range, for example from 1000 Da to 2000 Da equivalentweight, generally have unsaturations in the range of 0.03 to about 0.095meq/g.

To lower the unsaturation, and thus the monol content, various processparameters have been adjusted, such as the catalyst level andoxyalkylation temperature. However, improvement in the level ofunsaturation in such cases comes at the expense of process time.Moreover, the improvement is at best marginal. Use of alternativecatalyst systems, such as barium hydroxide, transparent iron oxides,diethyl zinc, metal phthalocyanines, and combinations of metalnaphthenates and tertiary amines have also been proposed, the lattermethod being able to reduce unsaturation to the range of 0.03 to 0.04meq/g in c.a. 4000 Da polyoxypropylene triols. However, even at thislower level, as compared to the 0.07 to 1.0 meq/g representative ofconventionally catalyzed but otherwise similar polyols, the mol percentmonol is still high, for example 25 mol percent or thereabouts.

Significant improvement in monol content of polyoxypropylene polyols hasbeen achieved using double metal cyanide catalysts, for example thenon-stoichiometric zinc hexacyanocobaltate-glyme catalysts disclosed inU.S. Pat. No. 5,158,922. Through use of such catalysts, polyoxypropylenepolyols of much higher molecular weight than previously thought possiblehave been prepared, for example 10,000 Da polyoxypropylene triols withunsaturations of 0.017 meq/g. J. W. Reish et al., "Polyurethane Sealantsand Cast Elastomers With Superior Physical Properties", 33RD ANNUALPOLYURETHANE MARKETING CONFERENCE, Sep. 30-Oct. 3, 1990, pp. 368-374.

Numerous patents have addressed the use of higher molecular weightpolyols to prepare polyurethanes. In such cases, the improvements aresaid to result either solely from the ability to provide highermolecular weight polyols of useful functionality, or additionally, thelow monol content, the monol thought to react as "chain-stoppers" duringpolyurethane addition polymerization. Illustrative examples of suchpatents are U.S. Pat. No. 5,124,425 (room temperature cure sealants fromhigh molecular weight polyols having less than 0.07 meq/g unsaturation);U.S. Pat. No. 5,100,997 (diamine extended polyurethane/urea elastomersfrom high molecular weight polyols having less than 0.06 meq/gunsaturation); U.S. Pat. No. 5,116,931 (thermoset elastomers from doublemetal cyanide catalyzed polyols having less than 0.04 meq/gunsaturation); U.S. Pat. No. 5,250,582 (high molecular weight DMC.glymecatalyzed polyols grafted with unsaturated polycarboxylic acids toprovide in situ blowing agent); U.S. Pat. No. 5,100,922 (high molecularweight polyols, preferably DMC.glyme catalyzed, together with aromaticcrosslinking agent useful in preparing integral skin foams); U.S. Pat.No. 5,300,535 (high molecular weight polyols with unsaturation less than0.07 meq/g useful in preparing foams with low resonant frequencies forseating applications); and U.S. Pat. No. 4,239,879 (elastomers based onhigh equivalent weight polyols). However, none of these patents addressprocessing characteristics, which are of paramount importance in thecast elastomer industry.

C. P. Smith et al., in "Thermoplastic Polyurethane Elastomers Made FromHigh Molecular Weight Poly-L™ Polyols", POLYURETHANES WORLD CONGRESS1991, Sep. 24-26, 1991, pp. 313-318, discloses thermoplastic elastomers(TPU) prepared from polyoxyethylene capped polyoxypropylene diols withunsaturation in the range of 0.014-0.018 meq/g. The polyols used wereprepared using double metal cyanide.glyme catalysts, and the elastomersshowed increased physical properties as compared to elastomers preparedfrom a conventionally catalyzed diol of 0.08 meq/g unsaturation.Additional examples of low unsaturation polyols in polyurethaneelastomers is given in "Comparison of the Dynamic Properties ofPolyurethane Elastomers Based on Low Unsaturation PolyoxypropyleneGlycols and Poly(tetramethylene oxide) Glycols", A. T. Chen et al.,POLYURETHANES WORLD CONGRESS 1993, Oct. 10-13, 1993, pp. 388-399. Citedas positively influencing elastomer physical properties were the lowmonol content and low polydispersity of the c.a. 0.015 meq/g, DMC.glymecatalyzed polyols used. Neither publication addresses processingcharacteristics, or the surprising effect that ultra-low unsaturationand broad polydispersity have on these characteristics.

It has been reported that low unsaturation polyols sometimes producepolyurethanes with anomalous properties. For example, the substitutionof a low unsaturation 10,000 Da molecular weight triol for a 6000 Damolecular weight conventionally catalyzed triol produced an elastomer ofhigher Shore A hardness where one would expect a softer elastomer,whereas substitution of a similarly DMC.glyme catalyzed 6000 Damolecular weight triol for a conventional 6000 Da molecular weight triolshowed no increase in hardness. R. L. Mascioli, "Urethane Applicationsfor Novel High Molecular Weight Polyols", 32ND ANNUAL POLYURETHANETECHNICAL/MARKETING CONFERENCE, Oct. 1-4, 1989. Moreover, and as morefully set forth below, butanediol extended elastomers prepared fromDMC.glyme catalyzed polyols exhibited demold times of 150 minutes ormore, which is commercially unacceptable in cast elastomer applications.

In copending U.S. application Ser. No. 08/156,534, herein incorporatedby reference, are disclosed novel double metal cyanide.t-butanol(DMC.TBA) catalysts prepared by intimate mixing of catalyst reactants.These catalysts lack the crystallinity characteristic of DMC.glymecatalysts as shown by X-ray diffraction studies, and moreover exhibitthreefold to tenfold higher activity in propylene oxide polymerization.It is especially surprising that the unsaturation is lowered tounprecedented ultra-low values through use of these catalysts, withmeasured unsaturations of from 0.003 meq/g to 0.007 meq/g routinelyachieved.

While the measurable unsaturation implies an exceptionally low butfinite monol content, it is especially surprising that analysis of theproduct polyols by gel permeation chromatography showed no detectablelow molecular weight fraction. The polyols are essentially monodisperse.The virtually complete absence of any low molecular weight speciesrenders such polyols different in kind from even those prepared fromDMC.glyme catalysts.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide polyurethaneelastomers with improved demold times and green strength.

It is a further object of the present invention to provide diol extendedpolyurethane elastomers which may be demolded in one hour or less.

It is a yet further object of the present invention to provide diolextended polyurethane elastomers which develop good green strength inone hour or less.

It is still a further object of the present invention to providepolyether polyol compositions which are uniquely adapted for preparingpolyurethane elastomers with improved demold and/or green strength whileretaining physical properties.

It has now been surprisingly discovered that a more than twofoldreduction in polyurethane elastomer demold time may be achieved throughthe use of predominately polyoxypropylene polyether polyols havingmeasured unsaturations of 0.010 meq/g polyol or less. It has furtherbeen surprisingly discovered that even further improvements in demoldtime are possible when the ultra-low unsaturation polyols have apolydispersity of 1.4 or greater.

It has further been discovered that microcellular elastomer formulationsexhibit a surprising decrease in shrinkage when the majority of thepolyether polyols used in their preparation are polyoxypropylene polyolshaving measured unsaturation of less than 0.010 meq/g.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a gel permeation chromatography trace of a polyoxypropylenetriol prepared in the presence of a DMC.glyme catalyst;

FIG. 2 is a gel permeation chromatography trace of a polyoxypropylenetriol similar to that of FIG. 1, but prepared in the presence of DMC.TBAcatalyst; and

FIG. 3 contains plots of storage modulus against temperature of apolyurethane elastomer prepared from an ultra-low unsaturation polyol ofthe subject invention and an elastomer prepared from a low unsaturationpolyol.

DESCRIPTION OF PREFERRED EMBODIMENTS

The polyurethane elastomers of the subject invention are prepared by thereaction of a di- or polyisocyanate, preferably a diisocyanate, with apolyoxyalkylene polyether polyol mixture by either the prepolymer,one-shot, or other techniques, using diols, or mixtures thereof as chainextenders. While the process of preparing polyurethane elastomers andthe raw materials which have been used in the past are well known tothose skilled in the art, reference may be had to the following materialfor purposes of basic reference.

By the term "polyurethane" is meant a polymer whose structure containspredominately urethane ##STR1## linkages between repeating units. Suchlinkages are formed by the addition reaction between an organicisocyanate group R-- --NCO! and an organic hydroxyl group HO--!--R. Inorder to form a polymer, the organic isocyanate and hydroxylgroup-containing compounds must be at least difunctional. However, asmodernly understood, the term "polyurethane" is not limited to thosepolymers containing only urethane linkages, but includes polymerscontaining minor amounts of allophanate, biuret, carbodiimide,oxazolinyl, isocyanurate, uretidinedione, urea, and other linkages inaddition to urethane. The reactions of isocyanates which lead to thesetypes of linkages are summarized in the POLYURETHANE HANDBOOK, GunterVertel, Ed., Hanser Publishers, Munich, ®1985, in Chapter 2, p. 7-41;and in POLYURETHANES: CHEMISTRY AND TECHNOLOGY, J. H. Saunders and K. C.Frisch, Interscience Publishers, New York, 1963, Chapter III, pp.63-118.

The urethane forming reaction is generally catalyzed. Catalysts usefulare well known to those skilled in the art, and many examples may befound for example, in the POLYURETHANE HANDBOOK, Chapter 3, §3.4.1 onpages 90-95; and in POLYURETHANE: CHEMISTRY AND TECHNOLOGY, in ChapterIV, pp. 129-217. Most commonly utilized catalysts are tertiary aminesand organotin compounds, particularly dibutyltin diacetate anddibutyltin dilautrate. Combinations of catalysts are often useful also.

In the preparation of polyurethanes, the isocyanate is reacted with theactive hydrogen-containing compound(s) in an isocyanate to activehydrogen ratio of from 0.5 to 1 to 10 to 1. The "index" of thecomposition is defined as the --NCO/active hydrogen ratio multiplied by100. While the extremely large range described previously may beutilized, most polyurethane processes have indices of from 70 to about120 or 130, more preferably from 95 to about 110, and most preferablyfrom 100 to 105. In calculating the quantity of active hydrogenspresent, in general all active hydrogen containing compounds other thannon-dissolving solids are taken into account. Thus, the total isinclusive of polyols, chain extenders, functional plasticizers, etc.

Hydroxyl group-containing compounds (polyols) useful in the preparationof polyurethanes are described in the POLYURETHANE HANDBOOK in Chapter3, §3.1, pages 42-61; and in POLYURETHANES: CHEMISTRY AND TECHNOLOGY inChapter II, §§III and IV, pages 32-47. Many hydroxyl-group containingcompounds may be used, including simple aliphatic glycols, dihydroxyaromatics, particularly the bisphenols, and hydroxyl-terminatedpolyethers, polyesters, and polyacetals, among others. Extensive listsof suitable polyols may be found in the above references and in manypatents, for example in columns 2 and 3 of U.S. Pat. No. 3,652,639;columns 2-6 of U.S. Pat. No. 4,421,872; and columns 4-6 of U.S. Pat. No.4,310,632; these three patents being hereby incorporated by reference.

Preferably used are hydroxyl-terminated polyoxyalkylene and polyesterpolyols. The former are generally prepared by well known methods, forexample by the base catalyzed addition of an alkylene oxide, preferablyethylene oxide (oxirane), propylene oxide (methyloxirane) or butyleneoxide (ethyloxirane) onto an initiator molecule containing on theaverage two or more active hydrogens. Examples of preferred initiatormolecules are dihydric initiators such as ethylene glycol,1,6-hexanediol, hydroquinone, resorcinol, the bisphenols, aniline andother aromatic monoamines, aliphatic monoamines, and monoesters ofglycerine; trihydric initiators such as glycerine, trimethylolpropane,trimethylolethane, N-alkylphenylenediamines, mono-, di-, andtrialkanolamines; tetrahydric initiators such as ethylene diamine,propylenediamine, 2,4'-, 2,2'-, and 4,4'-methylenedianiline,toluenediamine, and pentaerythritol; pentahydric initiators such asdiethylenetriamine and α-methylglucoside; and hexahydric and octahydricinitiators such as sorbitol and sucrose.

Addition of alkylene oxide to the initiator molecules may take placesimultaneously or sequentially when more than one alkylene oxide isused, resulting in block, random, and block-random polyoxyalkylenepolyethers. The number of hydroxyl groups will generally be equal to thenumber of active hydrogens in the initiator molecule. Processes forpreparing such polyethers are described both in the POLYURETHANEHANDBOOK and POLYURETHANES: CHEMISTRY AND TECHNOLOGY as well as in manypatents, for example U.S. Pat. Nos. 1,922,451; 2,674,619; 1,922,459;3,190,927; and 3,346,557. Preferable are polyether polyols havingexceptionally low levels of unsaturation, prepared using double metalcyanide complex catalysts as described infra.

Polyester polyols also represent preferred polyurethane-formingreactants. Such polyesters are well known in the art and are preparedsimply by polymerizing polycarboxylic acids or their derivatives, forexample their acid chlorides or anhydrides, with a polyol. Numerouspolycarboxylic acids are suitable, for example malonic acid, citricacid, succinic acid, glutaric acid, adipic acid, pimelic acid, azelaicacid, sebacic acid, maleic acid, fumaric acid, terephthalic acid, andphthalic acid. Numerous polyols are suitable, for example the variousaliphatic glycols, trimethylolpropane and trimethylolethane,α-methylglucoside, and sorbitol. Also suitable are low molecular weightpolyoxyalkylene glycols such as polyoxyethylene glycol, polyoxypropyleneglycol, and block and random polyoxyethylene-polyoxypropylene glycols.These lists of dicarboxylic acids and polyols are illustrative only, andnot limiting. An excess of polyol should be used to ensure hydroxyltermination, although carboxy groups are also reactive with isocyanates.Methods of preparation of such polyester polyols are given in thePOLYURETHANE HANDBOOK and in POLYURETHANES: CHEMISTRY AND TECHNOLOGY.

Also suitable as the polyol are vinyl polymer modified polyols. Suchpolymer polyols are well known to the art, and are prepared by the insitu polymerization of one or more vinyl monomers, preferablyacrylonitrile and/or styrene, in the presence of a polyether orpolyester polyol, particularly polyols containing a minor amount ofnatural or induced unsaturation. Methods of preparing polymer polyolsmay be found in columns 1-5 and in the Examples of U.S. Pat. No.3,652,639; in columns 1-6 and the Examples of U.S. Pat. No. 3,823,201;particularly in columns 2-8 and the Examples of U.S. Pat. No. 4,690,956;and in U.S. Pat. Nos. 4,524,157; 3,304,273; 3,383,351; 3,523,093;3,953,393; 3,655,553; and 4,119,586, all of which patents are hereinincorporated by reference.

Non-vinyl polymer modified polyols are also preferred, for example thoseprepared by the reaction of a polyisocyanate with an alkanolamine in thepresence of a polyol as taught by U.S. Pat. Nos. 4,293,470; 4,296,213;and 4,374,209; dispersions of polyisocyanurates containing pendant ureagroups as taught by U.S. Pat. No. 4,386,167; and polyisocyanuratedispersions also containing biuret linkages as taught by U.S. Pat. No.4,359,541. Other polymer modified polyols may be prepared by the in situsize reduction of polymers until the particle size is less than 20 μm,preferably less than 10 μm.

Many isocyanates are useful in the preparation of urethanes. Examples ofsuch isocyanates may be found in columns 8 and 9 of U.S. Pat. No.4,690,956, herein incorporated by reference. The isocyanates preferredare the commercial isocyanates toluene diisocyanate (TDI)methylenediphenylene diisocyanate (MDI), and crude or polymeric MDI.Other isocyanates which may be useful include isophorone diisocyanateand dimethylxylylidene diisocyanate. Other isocyanates may be found inthe POLYURETHANE HANDBOOK, Chapter 3, §3.2, pages 62-73 andPOLYURETHANES: CHEMISTRY AND TECHNOLOGY, Chapter II, §II, pages 17-31.

Modified isocyanates are also useful. Such isocyanates are generallyprepared through the reaction of a commercial isocyanate, for exampleTDI or MDI, with a low molecular weight diol or amine, polyoxyalkyleneglycol, alkanolamine, or by the reaction of the isocyanates withthemselves. In the former case, isocyanates containing urethane, biuret,or urea linkages are prepared, while in the latter case isocyanatescontaining allophanate, uretonimine, carbodiimide or isocyanuratelinkages are formed.

Chain extenders may also be useful in the preparation of polyurethanes.Chain extenders are generally considered to be low molecular weightpolyfunctional compounds or oligomers reactive with the isocyanategroup. Aliphatic glycol chain extenders commonly used include ethyleneglycol, diethylene glycol, propylene glycol, 1,4-butanediol,1,6-hexanediol hydroquinone bis(2-hydroxyethyl) ether (HQEE),cyclohexanedimethanol, and the like. Amine chain extenders includealiphatic monoamines but especially diamines such as ethylenediamine andin particular the aromatic diamines such as the toluenediamines and thealkylsubstituted (hindered) toluenediamines.

Other additives and auxiliaries are commonly used in polyurethanes.These additives include plasticizers, flow control agents, fillers,antioxidants, flame retardants, pigments, dyes, mold release agents, andthe like. Many such additives and auxiliary materials are discussed inthe POLYURETHANE HANDBOOK in Chapter 3, §3.4, pages 90-109 and inPOLYURETHANES: CHEMISTRY AND TECHNOLOGY, Part II, Technology.

Microcellular elastomers contain an amount of blowing agent which isinversely proportional to the desired foam density. Blowing agents maybe physical (inert) or reactive (chemical) blowing agents. Physicalblowing agents are well known to those in the art and include a varietyof saturated and unsaturated hydrocarbons having relatively lowmolecular weights and boiling points. Examples are butane, isobutane,pentane, isopentane, hexane, and heptane. Generally the boiling point ischosen such that the heat of the polyurethane-forming reaction willpromote volatilization.

Until recently, the most commonly used physical blowing agents were thehalocarbons, particularly the chlorofluorocarbons. Examples are methylchloride, methylene chloride, trichlorofluoromethane,dichlorodifluoromethane, chlorotrifluoromethane, chlorodifluoromethane,the chlorinated and fluorinated ethanes, and the like. Brominatedhydrocarbons may also be useful. Blowing agents are listed in thePOLYURETHANE HANDBOOK on page 101. Current research is directed tolowering or eliminating the use of chlorofluorocarbons, and followingthe Montreal Protocol, great strides have been made to reduce oreliminate completely, the use of chlorofluorocarbon (CFC) blowing agentswhich exhibit high ozone depletion potential (ODP) and global warmingpotential (GWP). As a result, many new halogenated blowing agents havebeen offered commercially. A preferred group are, for example, thehighly fluorinated alkanes and cycloalkanes (HFCs) and perfluorinatedalkanes and cycloalkanes (PFCs).

Chemical blowing agents are generally low molecular weight species whichreact with isocyanates to generate carbon dioxide. Water is the onlypractical chemical blowing agent, producing carbon dioxide in aone-to-one mole ratio based on water added to the foam formulation.Unfortunately, completely water-blown foams have not proven successfulin some applications such as rigid insulation and thus it is stillcommon to use water in conjunction with a physical blowing agent in somecases. Polyurethane high resilience microcellular elastomers are typicalall-water blown foams.

Blowing agents which are solids or liquids which decompose to producegaseous byproducts at elevated temperatures can in theory be useful, buthave not achieved commercial success. Air, nitrogen, argon, and carbondioxide under pressure can also be used in theory, but have not provencommercially viable. Research in such areas continues, particularly inview of the trend away from chlorofluorocarbons.

Polyurethane microcellular elastomers generally require a surfactant topromote uniform cell sizes and prevent foam collapse. Such surfactantsare well known to those skilled in the art, and are generallypolysiloxanes or polyoxyalkylene polysiloxanes. Such surfactants aredescribed, for example, in the POLYURETHANE HANDBOOK on pages 98-101.Commercial surfactants for these purposes are available from a number ofsources, for example from Wacker Chemie, the Union Carbide Corporation,and the Dow-Corning Corporation.

Processes for the preparation of polyurethane microcellular elastomersand the equipment used therefore are well known to those in the art, andare described, for example, in the POLYURETHANE HANDBOOK in Chapter 4,pages 117-160 and in POLYURETHANES: CHEMISTRY AND TECHNOLOGY, Part II,Technology, in Chapter VIII, §§III and IV on pages 7-116 and ChapterVIII, §§III and IV on pages 201-238.

With reference to the subject invention, the isocyanates useful in thepreparation of the subject elastomers may, in general, be any organicdi- or polyisocyanate, whether aliphatic or aromatic. However, preferredisocyanates are the commercially available isocyanates toluenediisocyanate (TDI) and methylenediphenylene diisocyanate (MDI). Toluenediisocyanate is generally used as an 80:20 mixture of 2,4- and 2,6-TDI,although other mixtures such as the commercially available 65:35 mixtureas well as the pure isomers are useful as well. Methylenediphenylenediisocyanate may also be used as a mixture of 2,4'-, 2,2'-, and 4,4'-MDIisomers. A wide variety of isomeric mixtures are commercially available.However, most preferable is 4,4'-MDI or this isomer containing only mostminor amounts of the 2,4'- and 2,2'-isomers, as the latter may oftenaffect physical properties in a manner not desirable for a particularproduct.

Preferred aliphatic isocyanates are the linear alkylene diisocyanatessuch as 1,6-diisocyanatohexane, 1,8-diisocyanatooctane, and lineardiisocyanates having interspersed heteroatoms in the alkylene residue,such as bis(3-isocyanatopropyl)ether. More preferred aliphaticisocyanates are the various cycloaliphatic isocyanates such as thosederived from hydrogenated aryldiamines such as toluene diamine andmethylenedianiline. Examples are 1-methyl-2,4-diisocyanatocyclohexaneand 1-methyl-2,6-diisocyanatocyclohexane;bis(4-isocyanatocyclohexyl)methane and isomers thereof; 1,2-, 1,3-, and1,4-bis(2-(2-isocyanato)propyl)benzene; and isophorone diisocyanate.

Modified isocyanates based on TDI and MDI are also useful, and many arecommercially available. To increase the storage stability of MDI, forexample, small quantities, generally less than one mole of an aliphaticglycol or modest molecular weight polyoxyalkylene glycol or triol may bereacted with 2 moles of diisocyanate to form a urethane modifiedisocyanate.

Also suitable are the well known carbodiimide, allophanate, uretonimine,biuret, and urea modified isocyanates based on MDI or TDI. Mixtures ofdiisocyanates and modified diisocyanates may be used as well. Ingeneral, the isocyanate index of the overall formulation is adjusted tobetween 70 and 130, preferably 90 and 110, and most preferably about100. Lower indexes generally result in softer products of lower tensilestrength and other physical properties, while higher indexes generallyresult in harder elastomers which require oven cure or cure for longperiods at ambient temperatures to develop their final physicalproperties. Use of isocyanate indexes appreciably above 130, for example200-300 generally require addition of a trimerization catalyst andresult in a crosslinked, less extensible elastomer having considerablepolyisocyanurate linkages.

The chain extenders useful in the subject invention elastomers arepreferably the aliphatic glycols and polyoxyalkylene glycols withmolecular weights up to about 500 Da, preferably 300 Da. Aromaticdihydroxy compounds such as hydroquinone, the bisphenols, and4,4'-dihydroxybiphenyl may be used as well. The chain extender may be asole chain extender or mixture. Preferred are ethylene glycol,diethylene glycol, propylene glycol, 1,3-propanediol,2-methyl-1,3-propanediol, butylene glycol, 1,4-butanediol,1,6-hexanediol, hydroquinone bis(2-hydroxyethyl) ether (HQEE),cyclohexanedimethanol (CHDM), 1,4-cyclohexanediol, and the like. Mostpreferred are ethylene glycol and in particular 1,4-butanediol and1,6-hexanediol.

Amine chain extenders may also be used, preferably in minor amount.Examples are ethylene diamine and 1,6-hexanediamine, anddiethylenetriamine among the aliphatic amine chain extenders. Suitablearomatic diamine chain extenders are the various toluenediamine isomersand their mixtures, the various methylenediphenylene diamines and theirmixtures, and preferably the slower reacting aromatic diamines such as4,4'-methylene bis(2-chloroaniline) (MOCA) and the sterically hinderedalkyl substituted toluenediamines and methylenediphenylene diamines.Also suitable are the amino-terminated polyethers such as thoseavailable commercially as Jeffamine® polyethers. The amine extendedelastomers generally exhibit a short demold time. However, in manyindustries, for example the automobile industry, where polyurethane/ureaelastomers are injected into complex molds to prepare automobile partssuch as fascias, further lowering the demold time and in particularincreasing green strength is important due to the minimal number of veryexpensive molds utilized. Preferably, however, the subject elastomersare polyurethane elastomers prepared with chain extenders consistingessentially of diols.

In the subject invention elastomers, it is the polyether polyolcomponent which is critical. Polyoxyalkylene polyether blends containingpolyoxypropylene polyols with exceptionally low unsaturation must beused and must be prepared with this low level of unsaturation. Themeasured unsaturation (ASTM test method D-2849-69) must be less than0.010 meq/g for the polyol blend. Furthermore, the individual polyols,regardless of the overall blend unsaturation, must have individualunsaturations of less than 0.015 meq/g. Preferred are polyol blendswhere the overall unsaturation is less than 0.007 meq/g and noindividual polyol has an unsaturation greater than 0.010. Most preferredis the use of individual polyols in the blend where each polyol has ameasured unsaturation of less than about 0.007 meq/g.

Thus, the major portion of the polyol blend, in order to have an overallunsaturation of less than 0.010 meq/g, must be an essentiallymonodisperse polyoxypropylene polyol which is preferably prepared bypolymerizing propylene oxide onto an initiator molecule of suitablefunctionality in the presence of a substantially amorphous double metalcyanide.TBA catalyst such as those prepared as disclosed in copendingU.S. application Ser. No. 08/156,534, which is herein incorporated byreference. Examples of catalyst preparation and polyol preparation aregiven in the Referential Examples herein.

In FIG. 1 is shown a GPC trace of a "low unsaturation" polyoxypropylenetriol prepared using a DMC.glyme catalyst as disclosed in U.S. Pat. No.5,158,922. Even though the unsaturation is considerably lower than thosedisclosed, for example, by U.S. Pat. No. 5,106,874, notable is the lowmolecular weight peak centered at approximately 21 minutes. In FIG. 2 isillustrated an ultra-low unsaturation polyol prepared by the DMC.TBAcatalyst as disclosed in U.S. application Ser. No. 08/156,534, and theReferential Examples of the present application. It is notable that thispolyol is essentially monodisperse, i.e. there is no detectable lowmolecular weight component. Notable also is the symmetry of the GPC peakwhich does not show any appreciable tailing due to lower molecularweight components. This polyoxypropylene polyol has a measuredunsaturation of only about 0.005 meq/g, however, the two polyols areotherwise analytically similar in terms of average molecular weight andfunctionality.

The polyol of FIG. 1 has a monol content of from 5-10 mol percent, ascompared to conventional, base catalyzed polyols where the monol contentfor a polyol in this molecular weight range is commonly from 25-35 molpercent. It is not surprising, therefore, that the polyols of FIG. 1,with their higher average functionality and lower monol content, wouldrespond differently than the conventionally catalyzed polyols of muchhigher monol content. However, it is highly surprising that theultra-low unsaturation polyoxypropylene polyols of the subject inventionwould behave so differently from low unsaturation polyols havingunsaturation in the range of 0.014 to 0.018 meq/g, as the monol contentof these polyols is already very low. In particular, it was mostsurprising that elastomers prepared from the latter polyols exhibiteddemold times in excess of 150 minutes, while elastomers prepared fromthe subject ultra-low unsaturation polyols, in similar formulations,exhibited demold of 60 minutes or less, an improvement of 150%|

The polyether polyols useful in the subject invention are preferablyprepared by polymerizing propylene oxide or a mixture of propylene oxideand another alkylene oxide having more than 2 carbon atoms, for example,1,2-butylene oxide, 2,3-butylene oxide, oxetane, or tetrahydrofuran,onto a suitably functional initiator molecule, in the presence of acatalytically effective amount of a substantially amorphous double metalcyanide.TBA catalyst, preferably zinc hexacyanocobalt.TBA. Othersynthetic methods which result in ultra-low unsaturations of less than0.010 meq/g, preferably 0.007 meq/g or less are also suitable. By theterm "polyoxypropylene polyol" and like terms is meant a polyol whereinthe major portion of oxyalkylene groups are oxypropylene groups.

If a most minor amount of ethylene oxide, or if another alkylene oxide,for example, butylene oxide, is to be copolymerized with propylene oxidein random (heteric) fashion, the two alkylene oxides may simply be addedsimultaneously to the pressurized reactor. Surprisingly, this processcannot, at present, be utilized to provide polyoxyethylene cappedpolyoxypropylene homo or random copolymers, but rather, ethylene oxidedesired to be added as a cap should be polymerized in the presence of analternative catalyst, preferably an alkali metal hydroxide.

The amount of randomly copolymerized ethylene oxide should be mostminor, i.e. from 0 to about 1% or thereabouts, as the polyol backboneshould be substantially all polyoxypropylene or polyoxypropylenecopolymerized with another alkylene oxide having more than two carbonatoms. Ethylene oxide derived moieties may be present as a cap whenblends of polyols are utilized as described herein or in microcellularelastomers, and in such cases it is preferable that the weight percentof such cap be from 3 weight percent to about 30 weight percent,preferably 5 weight percent to 25 weight percent, and most preferablyfrom about 10 weight percent to about 20 weight percent based on theweight of the finished polyol. For purposes of preparation of low waterabsorption elastomers, it is preferred that the total ethylene oxidecontent of the polyol, both external (cap) and any minor internaloxyethylene moieties, be less than 15 weight percent, more preferablyless than 10 weight percent. Preferably, all propylene oxide-derivedpolyoxypropylene polyols are used.

Polyoxypropylene polyols, whether catalyzed by DMC.glyme or DMC.TBAcatalysts, in general, have a very low, or narrow, polydispersity. Thepolydispersity of a polymer or polymer blend may be defined by the ratioof Mw/Mn where Mw is the weight average molecular weight and Mn is thenumber average molecular weight. The weight average molecular weight isdefined as Mw=Σ_(i) ω_(i) M_(i) where M_(i) is the ith molecular weightand ω_(i) is the weight fraction in the total of the ith molecularweight component. The number average molecular weight is defined asΣ_(i) n_(i) M_(i) where M_(i) is defined as above and n_(i) is thenumber fraction of the total of the ith molecular weight component. Fora theoretically perfect monodisperse polymer where all polymeric specieshave a single molecular weight, M_(w) =M_(n) and the polydispersityM_(w) /M_(n) =1. In practice, true monodispersity is never achieved, andin the subject application, polymers described as monodisperse havepolydispersities close to 1, for example 1.20 or less, and preferably1.10 or less. The molecular weights reported herein are number averagemolecular weights.

The term "multidisperse" as used herein indicates a bi- or trimodal,etc. distribution of molecular weights, with each individualdistribution being essentially monodisperse. Such multidisperse blendsare advantageously prepared by mixing two or more essentiallymonodisperse polyols, or by introduction of a second portion of the sameor different initiator molecule into the polymerization in the presenceof a DMC.TBA catalyst.

The polydispersities of a blend of two polyols can be calculated usingthe following equations:

    Mw.sub.blend =Mw.sub.1 α.sub.1 +Mw.sub.2 α.sub.2,

    Mn.sub.blend =Mn.sub.1 Mn.sub.2 /(Mn.sub.1 α.sub.2 +Mn.sub.2 α.sub.1),

    Polydispersity.sub.blend =Mw.sub.blend /Mn.sub.blend,

where Mw₁ and Mw₂ are weight average molecular weights, Mn₁ and Mw₂ arenumber average molecular weights, and α₁ and α₂ are weight fractions ofpolyols 1 and 2, respectively.

The DMC.TBA catalyzed polyols prepared at normal catalyst levels, arevery nearly truly monodisperse, with the molecular weights of thevarious molecules concentrated within a tight band with virtually nodetectable lower molecular weight species. The polydispersity of suchpolyols is generally less than about 1.2. It has been surprisinglydiscovered that further improvements in demold time and green strengthmay be achieved if the polydispersity of the polyoxyalkylene polyol isgreater than 1.4, while the level of unsaturation is maintained, asbefore, at less than 0.010 meq/g. This greater polydispersity may beaccomplished in several ways.

If very low amounts of double metal cyanide catalysts are utilized inthe propylene oxide polymerization, polyoxypropylene polyols may beobtained which, as is the case with normal levels of catalyst, have alevel of unsaturation less than 0.010 meq/g, but which have a muchbroader molecular weight distribution than analogous polyols prepared athigher catalyst levels. These polyols are monomodal in the sense thatthey contain only a single, albeit broad, peak by GPC. However, theirpolydispersity, Mw/Mn is greater than 1.4, and preferably greater than2.0. The latter polyols, having polydispersity greater than 2.0 whileretaining very low unsaturation and a monomodal molecular weightdistribution, are novel products.

A second, and preferred method of preparing ultra low unsaturationpolyols with polydispersities greater than 1.4 is to blend two or moreultra-low unsaturation polyols with low polydispersity but differentmolecular weights, for example a blend of a 1000 Da diol with an 8000 Dadiol, or a blend of a 2000 Da diol, 4000 Da diol, and 8000 Da diol. Insuch cases, the blends may be termed multidisperse, as they have abimodal, trimodal, etc., molecular weight distribution. Thepolydispersity Mw/Mn of the blends are preferably greater than 1.4, andmay suitably be greater than 1.8 or 2.0, or higher. Each of theindividual polyols in the blend has a polydispersity preferably lessthan 1.2.

It is most surprising that such blends exhibit demold times much lowerthan a monodisperse polyol with low polydispersity. For example, a 2000Da average molecular weight multidisperse polyoxypropylene diol derivedelastomer where the diol component is a blend of monodisperse 1000 Daand 4000 Da diols exhibited a demold time of only 21 minutes, ascompared to an otherwise similar elastomer containing a single,monodisperse 2000 Da diol which exhibited a demold time of 45 minutes.In addition, the elastomer containing the ultra-low unsaturation,multidisperse 2000 Da diol exhibited a surprising improvement in greenstrength. It is further highly surprising that a 4000 Da averagemolecular weight blend of a conventionally catalyzed 1000 Dapolyoxypropylene diol having a conventional level of unsaturation withan ultra-low unsaturation polyol having a molecular weight of 8000 Daand an unsaturation of only 0.005 meq/g failed to provide anyimprovement in demold time compared to a straight 4000 Da ultra-lowunsaturation polyol with unsaturation of 0.005 meq/g despite the factthat the blend had an average unsaturation of 0.007 meq/g, showing theimportance of low unsaturation in both components and not merely theoverall unsaturation of the blend. The elastomer from the blend ofconventional diol and ultra-low unsaturation diol also displayed poorgreen strength relative to otherwise similar blends where both polyolshave ultra-low unsaturation.

The polyol blends useful in the subject invention includepolyoxyalkylene polyols having equivalent weights of from 400 Da to10,000 Da or higher, preferably 400 Da to 8000 Da, and more preferably500 Da to 8000, providing polyol components having average equivalentweights in the range of 1000 Da to 8000 Da. The ultra-low unsaturationpolyols of the subject invention may have nominal (i.e. initiator)functionalities from 2 to 8, preferably 2 to 6, and most preferably 2 to3. Diols or mixtures of diols and triols are preferred, particularlypolydisperse blends of monodisperse diols, while in some formulationsadditions of minor portions of tetrols or hexols, for example, may leadto increases in desirable properties. Suitable initiators are well knownto those skilled in the art, and include, for example, ethylene glycol,propylene glycol, 1,4-butanediol, glycerine, trimethylolpropane,pentaerythritol, α-methylglucoside, sorbitol, sucrose, ethylene diamine,propylene diamine, toluenediamine, diethylenetriamine, and the like. Inpreparing the ultra-low unsaturation polyols, the chosen initiator orinitiator mixture is generally first oxyalkylated with a non-DMCcatalyst to a low molecular weight polyoxyalkylene oligomer having anequivalent weight in the range of 200-400 Da, although lower and highermolecular weight oligomers may be used.

The elastomers may advantageously be prepared from anisocyanate-terminated prepolymer prepared by the reaction of amonodisperse polyoxypropylene diol having a molecular weight of from1000 Da to about 20,000 Da, a polydispersity of about 1.20 or less, andan unsaturation of 0.008 meq/g or less. Microcellular elastomersprepared from such compositions preferably have densities of less thanabout 0.80 g/cm³, and exhibit demold times of 60 minutes or less.

Preferably, the elastomers are prepared by the prepolymer process,however, the one shot process is useful as well. In the prepolymerprocess, the polyoxyalkylene polyol mixture is reacted with excess di-or polyisocyanate to form an isocyanate-terminated prepolymer containingfrom about 1% to about 25% by weight NCO groups, preferably from about3% to about 12% NCO, more preferably about 4 to about 10% NCO, and mostpreferably about 6% NCO. Prepolymer preparation may be catalyzed,preferably by tin catalysts such as dibutyltin diacetate and dibutyltindilaurate, in amounts of from 0.001 to about 5%, and more preferably0.001 to about 1% by weight. The manufacture of prepolymers is withinthe level of skill in the art. If desired, the prepolymer polyolcomponent may be augmented with hydroxyl-functional polyols other thanpolyoxyalkylene polyols, for example polyester polyols, polycaprolactonepolyols, polytetramethylene ether glycols (PTMEG), and the like.

Following prepolymer formation, the prepolymer is then mixed with aproportion of one or more chain extenders such that the isocyanate indexis in the desired range. The prepolymer and chain extender arethoroughly mixed, degassed if necessary, and introduced into the propermold or, if thermoplastic polyurethanes are desired, reaction extrudedand granulated or deposited on a moving belt and subsequentlygranulated.

Preferred chain extenders are the aliphatic and cycloaliphatic glycolsand oligomeric polyoxyalkylene diols. Examples of suitable aliphaticglycol chain extenders are ethylene glycol, diethylene glycol, 1,2- and1,3-propanediol, 2-methyl-l,3-propanediol, 1,2- and 1,4-butane diol,neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanediol,1,4-cyclohexanedimethanol, hydroquinone bis(2-hydroxyethyl) ether, andpolyoxyalkylene diols such as polyoxyethylene diols, polyoxypropylenediols, beteric and block polyoxyethylene/polyoxypropylene diols,polytetramethylene ether glycols, and the like, with molecular weightsup to about 300 Da. Preferred are 1,6-hexanediol and 1,4 -butanediol,the latter particularly preferred.

Diamine chain extenders, for example the amine-terminatedpolyoxyalkylene polyethers sold under the tradename Jeffamine™, andparticularly the slower reacting deactivated or sterically hinderedaromatic diamines such as 3,5-diethyltoluenediamine and4,4'-methylenebis(2-chloroaniline) (MOCA) may be used, but generallyonly in most minor amounts. The advantageous effects of the subjectpolyol blends with diamine chain extenders is more difficult toquantify, as these systems are especially formulated for exceptionallyshort demold. Mixtures of aliphatic or cycloaliphatic diol chainextenders with diamine chain extenders may be used. When any significantamount of diamine is used, high pressure reaction injection moldingtechniques should be utilized.

The subject elastomers are highly suitable for microcellular elastomers,for example those suitable for use in shoe soles. The formulations ofsuch elastomers contain a minor amount of reactive or volatile blowingagent, preferably the former. For example, a typical formulation willcontain from about 0.1 to about 1.0 weight percent, preferably fromabout 0.2 to about 0.4 weight percent water. Isocyanate terminatedprepolymers are generally utilized in such formulations, and have higherNCO content, in general, than the prepolymers used to form non-cellularelastomers. Isocyanate group contents of from 8 to 25 weight percent,more preferably 10 to 22 weight percent, and most preferably 13-15weight percent are suitable. The formulations are generally crosslinkedand diol extended, the crosslinking being provided by employing, inaddition to the glycol chain extender, a tri- or higher functional, lowunsaturation polyol in the B-side, optionally also with a low molecularweight cross-linker such as diethanolamine (DEOA). Alternatively, theisocyanate-terminated prepolymer may be prepared from a tri- or higherfunctional low unsaturation polyol or a mixture of di- and higherfunctional low unsaturation polyols. All the polyols utilized insignificant amount in the formulation, whether incorporated intoprepolymer or in the B-side, should have unsaturations of 0.015 meq/g orless, preferably 0.010 meq/g or less, and the total average unsaturationof all polyol components on a molar basis should also be below 0.010meq/g, preferably 0.007 meq/g or less. In addition to taking advantagesof the shorter demold times and higher green strength, it is mostsurprising that the use of the subject polyols and polyol blendsproduces microcellular elastomers having sharply reduced shrinkage, aphysical property of paramount importance in the polyurethanemicrocellular elastomer shoe sole industry.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

Referential Example: Catalyst Preparation

Preparation of Zinc Hexacyanocobaltate Catalysts by Homogenization WithTert-butyl Alcohol as the Complexing Agent

A double metal cyanide-TBA catalyst is prepared by the method disclosedin copending U.S. application Ser. No. 08/156,534.

Potassium hexacyanocobaltate (8.0 g) is added to deionized water (150mL) in a beaker, and the mixture is blended with a homogenizer until thesolids dissolve. In a second beaker, zinc chloride (20 g) is dissolvedin deionized water (30 mL). The aqueous zinc chloride solution iscombined with the solution of the cobalt salt using a homogenizer tointimately mix the solutions. Immediately after combining the solutions,a mixture of tert-butyl alcohol (100 mL) and deionized water (100 mL) isadded slowly to the suspension of zinc hexacyanocobaltate, and themixture is homogenized for 10 minutes. The solids are isolated bycentrifugation, and are then homogenized for 10 minutes with 250 mL of a70/30 (v:v) mixture of tert-butyl alcohol and deionized water. Thesolids are again isolated by centrifugation, and are finally homogenizedfor 10 minutes with 250 mL of tert-butyl alcohol. The catalyst isisolated by centrifugation, and is dried in a vacuum oven at 50° C. and30 in. (Hg) to constant weight.

ReferentiaI Example:

Polyether Polyol Synthesis: Effect of Catalyst on Polyol Unsaturation

Polyoxypropylene polyols are prepared using the catalyst of ReferentialExample 1.

A two-gallon stirred reactor is charged with a glycerine initiatedpolyoxypropylene triol (700 Da mol. wt.) starter (685 g) and zinchexacyanocobaltate catalyst (DMC.TBA) (1.63 g) as prepared in the priorreferential example. The mixture is stirred and heated to 105° C., andis stripped under vacuum to remove traces of water from the triolstarter. Propylene oxide (102 g) is fed to the reactor, initially undera vacuum of 30 in. (Hg), and the reactor pressure is monitoredcarefully. Additional propylene oxide is not added until an acceleratedpressure drop occurs in the reactor; the pressure drop is evidence thatthe catalyst has become activated. When catalyst activation is verified,the remaining propylene oxide (5713 g) is added gradually over about 2hwhile maintaining a reactor pressure less than 40 psi. After propyleneoxide addition is complete, the mixture is held at 105° C. until aconstant pressure is observed. Residual unreacted monomer is thenstripped under vacuum from the polyol product. The hot polyol product isfiltered at 100° C. through a filter cartridge (0.45 to 1.2 microns)attached to the bottom of the reactor to remove the catalyst. Thepolyoxypropylene triol has a hydroxyl number of 27 and an unsaturationof only 0.005 meq/g. A similar triol prepared using a DMC.glyme catalystof the prior art had a hydroxyl number of 27 and an unsaturation of0.017 meq/g. A polyoxypropylene diol prepared from the DMC.TBA catalystusing a 450 Da polyoxypropylene glycol starter had a hydroxyl number of14 and an unsaturation of 0.004 meq/g.

The polyol was subjected to GPC analysis. The GPC trace is illustratedin FIG. 2. The polyol is monodisperse with no detectable lower molecularweight components, while the DMC.glyme catalyzed polyol had asignificant amount of such components.

Examples 1-2 and Comparative Examples A-D

A series of 6% NCO terminated prepolymers were prepared from 2000 and4000 Da diols prepared with either DMC.TBA catalyst (subject invention)or DMC.glyme catalysts (comparative). The measured unsaturation, demoldtimes, and green strength, where applicable, are presented in Table 1below. Green strength was not measured where demold times are greaterthan 150 minutes as such compositions are not commercially acceptabledue to the long demold time. All formulations had a pot life of from 3-5minutes. It is important, when comparing formulations, to compareformulations with similar pot life. The prepolymers were heated to 60°C. prior to adding chain extender, which was at room temperature.Dibutyltin dilaurate at 15 ppm was used as the urethane promotingcatalyst.

                  TABLE 1                                                         ______________________________________                                        Processing Characteristics of Elastomers                                      Made With Polyols Prepared With DMC Catalysts                                 (6% NCO MDI Prepolymer/BDO Extended)                                          Exam- Polyol    Polyol  Unsaturation                                                                          Demold Time                                                                            Green                                ple   Catalyst  MW      (meq/gm)                                                                              (minutes)                                                                              Strength                             ______________________________________                                        1     DMC--TBA  2000    0.005   45       fair                                 2     DMC--TBA  4000    0.005   60       fair                                 A     DMC-glyme 2000    0.014   >150     n.d.*                                B     DMC-glyme 2000    0.013   >150     n.d.*                                C     DMC-glyme 4000    0.014   >150     n.d.*                                D     DMC-glyme 4000    0.010   >150     n.d.*                                ______________________________________                                         *Not determined because sample could not be demolded within 150 minutes. 

Table I clearly indicates the dramatic reduction in demold time whenusing ultra-low unsaturation polyoxypropylene homopolymer diols for usein polyurethane elastomers. Not even Comparative Example D yields anacceptable demold time despite having an unsaturation of 0.010 meq/g.Clearly, the unsaturation must be less than 0.010 meq/g when using asingle polyoxypropylene polyol to prepare polyurethane elastomers havingacceptable demold time.

                  TABLE 2                                                         ______________________________________                                        Elastomer Properties Using the 4000 MW Diols                                  Prepared With DMC Catalysts                                                   (6% NCO MDI Prepolymer/BDO Extended)                                          EXAMPLE            1        C        D                                        ______________________________________                                        Polyol Unsaturation (meq/gm)                                                                     0.005    0.014    0.010                                    Prepolymer Viscosity (cps) @ 20° C.                                                       6380     5590     6670                                     Prepolymer Viscosity (cps) @ 80° C.                                                       380      310      370                                      Hardness (Shore A)  71      61(57)*  65(63)*                                  Rebound (%)         68       60       64                                      Elongation (%)     953      607      878                                      Tensile Strength (psi)                                                                           3320     1180     1840                                     100% Modulus (psi) 440      341      346                                      300% Modulus (psi) 880      685      674                                      Die C Tear Strength (pli)                                                                        374      220      272                                      ______________________________________                                         *Shore hardness needle penetrated slowly into the sample.                

In Table 2 are presented the physical properties of the elastomers fromTable 1 prepared from 4000 Da diols. Table 2 indicates that elastomersprepared from ultra-low unsaturation polyols have greatly improvedproperties as compared to those prepared from higher but still lowunsaturation analogs. All the measured physical properties of elastomersprepared from ultra-low unsaturation diols having unsaturations lessthan 0.010 meq/g are significantly higher than the physical propertiesof elastomers prepared from polyols having low but higher unsaturation.

The elastomer of Example 2 and Comparative Example C were subjected todynamic mechanical thermal analysis. As shown in FIG. 3, in the firstcurve, delineated by letters A-D, the storage modulus of an elastomer ishigh at low temperatures (A) due to the temperature being below the softsegment glass transition temperature T_(g)(SS). As the elastomertemperature passes T_(g)(SS), its rigid, glassy nature undergoes atransition to the rubbery state (B) and the storage modulus decreasesrapidly, until a relatively flat plateau is reached. Elastomericbehavior is obtained in the region of the plateau (C), until thetemperature reaches the melt temperature or softening temperature (D) ofthe hard segments T_(m)(HS). At this point, the elastomer begins tosoften and flow. While in theory the useful elastomeric range is betweenT_(g)(SS) and T_(m)(HS), in practice, it is limited to an uppertemperature of approximately 80° C. Extension of the lower range bylowering T_(g)(SS) results in an elastomer useable at lower temperature.

In the second curve is shown DMTA analysis of a second elastomer havinga higher T_(g)(SS) and a plateau which displays a steeper slope. Theslope of the plateau determines how well a particular elastomer retainsits physical properties with increasing temperature. In general, it isdesired that an elastomer have the same degree of flexibility at lowtemperatures and high temperatures within its use range, for example.

A further important property is the loss modulus, which is a measure ofthe energy loss of the elastomer due to the flow character or component.The ratio of loss modulus to storage modulus is the loss tangent delta(Tan Delta) which is related to the elastomer's dynamic performance. Thelower the loss tangent delta, the lower the heat buildup of theelastomer under dynamic stress. This property is particularly importantin applications where the elastomer is continually flexed or compressed,for example in jounce bumpers of front wheel drive vehicles.

Table 3 illustrates the T_(g)(SS), elastomeric plateau slope between 20°C. and 120° C., and the loss tangent delta of an ultra-low unsaturation(0.005 meq/g) polyol-derived elastomer and a similar polyol-derivedelastomer prepared from a polyol having an unsaturation of c.a. 0.015meq/g. As can be seen from the Table, the ultra-low unsaturationpolyol-derived elastomer has a much lower slope in the region of theplateau, indicating a much slower drop off in physical properties ascompared to an analogous elastomer prepared from a low but higherunsaturation polyol. The loss tangent delta of the subject inventionelastomer is also much lower (less than half) of that of the comparativeelastomer, lowering heat buildup substantially. Finally, the subjectinvention elastomer extends the low temperature elastomeric range by 2°C.

                  TABLE 3                                                         ______________________________________                                        Thermal and Dynamic Properties of Polyurethane                                Elastomers Based on 4000 Da Diols                                             (6% MDI Prepolymers/BDO Cured)                                                Polyol                                                                        Unsaturation                                                                          T.sub.g(SS) (°C.)                                                                 20° C./120° C.                                                             Tan Delta @ 20° C.                       ______________________________________                                        0.015 meq/g                                                                           -43        7.6        0.120                                           0.005 meq/g                                                                           -45        4.2        0.057                                           ______________________________________                                    

Examples 3 and 4

Two similar 6% NCO prepolymers were prepared, both from ultra-lowunsaturation polyoxypropylene diols, prepared as disclosed in thereferential examples. In Example 3, a 2000 Da molecular weight,monodisperse diol was utilized, while in Example 4, a blend of 1000 Daand 4000 Da diols having an average molecular weight of 2000 Da wereutilized. The prepolymers were chain extended with 1,4-butanediol asbefore. Example 3 showed a demold time of 45 minutes, a considerableimprovement over elastomers prepared from polyols having unsaturation of0.010 or higher where the demold time was greater than 150 minutes. Evenmore surprising was the improvement in green strength. Overall, theelastomer physical/mechanical properties were retained.

However, the 2000 Da molecular weight 1000 Da/4000 Da multidisperseblend surprisingly exhibited a demold time of only 21 minutes, less thanhalf of the monodisperse diol. Moreover, elongation, tensile strength,and tear strength were markedly improved, with only the modulusproperties being slightly lower. In addition, green strength wasimproved. The processing characteristics and physical properties are setforth in Table 4 below.

                  TABLE 4                                                         ______________________________________                                        Effect of Polyol Molecular Weight Distribution                                on Elastomer Processing and Properties                                        (6% NCO MDI Prepolymer/BDO Extended; 105 Index)                                                Example 3                                                                            Example 4                                             ______________________________________                                        Polyol Molecular Weight                                                                          2000     2000                                                                          (1000/4000 Blend)                                 Dispersity         mono-    multidisperse                                                        disperse                                                   Polydispersity (Mw/Mn)                                                                           1.05*     1.72**                                           Unsaturation (meq/gm)                                                                            0.005    0.005                                             PROCESSING CHARACTERISTICS                                                    Demold Time (minutes)                                                                             45       21                                               Green Strength     fair     good                                              PHYSICAL PROPERTIES                                                           Hardness (Shore A)  68       69                                               Rebound (%)         61       59                                               Elongation (%)     528      732                                               Tensile Strength (psi)                                                                           2060     2370                                              100% Modulus (psi) 480      430                                               300% Modulus (psi) 990      840                                               Die C Tear Strength (pli)                                                                        281      302                                               ______________________________________                                         *Determined by gel permeation chromatography (GPC).                           **Calculated based on GPC of individual components.                      

Examples 5-7 and Comparative Examples E-G

A further series of elastomers were prepared as before, with the amountof dibutyltin dilaurate catalyst adjusted to give similar pot lives,necessary in order to compare elastomer processing. The averagemolecular weight of all polyols or polyol blends was 4000 Da. In Example5, a monodisperse, ultra-low unsaturation 4000 Da diol was used, whereasin Examples 6 and 7, blends of ultra-low unsaturation 2000 Da and 8000Da diols, and DMC.TBA catalyzed 1000 Da and 8000 Da diols were used,respectively. The total average unsaturation of both blends was 0.005meq/g. In Comparative Example E, an 8000 Da ultra-low unsaturation(0.005 meq/g) diol was blended with a conventionally catalyzed 2000 Dapolyoxypropylene diol with an unsaturation of 0.026 meq/g. This diolblend had an average unsaturation of 0.012 meq/g. In Comparative ExampleF, the same 8000 Da ultra-low unsaturation diol was blended with aconventionally catalyzed polyoxypropylene glycol of c.a. 1000 Damolecular weight (0.015 meq/g). The blend of Comparative Example F hadan average unsaturation of only 0,007 meq/g due to the relatively smallamount of low molecular weight polyoxypropylene diol present. InComparative Example G, a blend similar to that of Comparative Example Fwas prepared, but the 8000 Da diol was a DMC.glyme catalyzed polyol. Theaverage unsaturation of the blend was 0,015 meq/g. The processingparameters and physical properties are tabulated in Table 5 below.

                                      TABLE 5                                     __________________________________________________________________________    Effect Of 4000 MW PPG Diol Blends On The Elastomer                            Processing Parameters (6% MCO MDI Prepolymers; BDO Extended)                  EXAMPLE             5    6     7     E     F     G                            __________________________________________________________________________    Polyol Type         4000 8000.sup.1 /2000.sup.1                                                              8000.sup.1 /1000.sup.1                                                              8000.sup.1 /2000.sup.2                                                              8000.sup.1 /1000.sup.2                                                              8000.sup.3 /1000.sup.2       Polydispersity (Mw/Mn)                                                                            1.15 1.71  2.06  1.73  1.90  1.90                         Average Unsaturation (meq/gm)                                                                     0.005                                                                              0.005 0.005 0.012 0.007 0.015                        Polyol Viscosity @ 23° C., cps                                                             1,100                                                                              2,500 3,450 n.d.* n.d.* n.d.*                        ELASTOMER PROCESSING PARAMETERS                                               Prepolymer Viscosity @ 20° C., cps                                                         8,220                                                                              12,980                                                                              17,480                                                                              n.d.* n.d.* n.d.*                        Prepolymer Viscosity @ 80° C., cps                                                         400  580   790   n.d.* n.d.* n.d.*                        Pot Life, seconds   124  124   124   94    110   88                           Demold Time, minutes                                                                              22   19    12    14    22    30                           Green Strength @ Demold                                                                           poor good  good  poor  poor  poor                         Green Strength @ 60 minutes                                                                       average                                                                            excellent                                                                           excellent                                                                           good  good  poor                         ELASTOMER PHYSICAL PROPERTIES                                                 Hardness, Shore A   71   68    71    70    70    66                           Resilience, %       68   64    66    64    64    63                           Elongation, %       903  867   890   908   943   540                          Tensile Strength, psi                                                                             2960 2625  2764  1954  1901  1046                         100% Modulus, psi   472  466   486   446   419   428                          300% Modulus, psi   896  880   873   791   748   760                          Die C Tear Strength, pli                                                                          362  349   366   311   315   287                          __________________________________________________________________________     .sup.1 Ultralow unsaturation, monodisperse polyoxypropylene diol of           subject invention                                                             .sup.2 Conventionally basecatalyzed high unsaturation polyoxypropylene        diol                                                                          .sup.3 DMC.glyme catalyzed polyoxypropylene diol                              *n.d. = not determined                                                   

Table 5 illustrates that it is not merely the average overallunsaturation which is important, c.f. Comparative Example F, but thateach significant polyol in the formulation must have a low degree ofunsaturation in addition to the blend having a low average unsaturation.The table further indicates that physical properties of elastomersprepared from all ultra-low unsaturation polyols are greatly enhanced aswell. Particularly noted in this respect are the tensile strength, 300%modulus, and Die C tear strengths.

In order to better quantify the green strength of these elastomers, thebuild in elastomer properties with time was measured while curing at100° C. This was done by simply removing the elastomer samples from theoven and quickly measuring the Shore A hardness and resilience at 100°C. The property build was measured through the first two hours of cure.Surprisingly, the Shore A hardness and resilience increase much fasterwith the multidisperse, ultra-low unsaturation polyols of the subjectinvention than with the monodisperse, ultra-low unsaturation polyol. Forexample, the elastomer based on the 8000 Da/1000 Da blend achieved 95%of its final Shore A hardness and 86% of its final resilience after only120 minutes versus 62% and 57%, respectively, for the monodisperse 4000Da polyol.

A series of microcellular elastomers were prepared to demonstrate theunexpected improvement resulting from the use of the ultra-lowunsaturation polyols of the present invention. Microcellular elastomersin accordance with the present invention are derived from a prepolymercomponent prepared using a substantial quantity of polyoxypropylenediol, preferably representing at least 20 weight percent of the totalpolyol, preferably greater than 30 weight percent, and most preferablyabout 50 weight percent. Prepolymers prepared from diols and triols arepreferred.

Example 8--Comparative Examples H and I

Three microcellular elastomers suitable for use in shoe soles were madeusing prepolymer diols and triols. The prepolymers were prepared in a2000 ml resin kettle equipped with a stirrer and nitrogen purge, intowhich 1199.4 g of the respective polyol and 0.04 g 85% phosphoric acidwere added. Then, 515.2 g Mondur® M 4,4'-diphenylmethane diisocyanatewas added and the mixture heated to 90° C. and stirred for c.a. 5 hours.The free NCO contents of the products were determined by titration to bebetween 8.2 and 8.5 weight percent. The polyols used in ComparativeExample H were PPG 4025, a conventionally base catalyzed nominal 4000 Dapolyoxypropylene diol and LHT-28, a 6000 Da average molecular weight,conventionally base catalyzed, glycerine initiated polyoxypropylenetriol. The polyols used in Comparative Example I were a 4000 Damolecular weight DMC.glyme catalyzed polyoxypropylene diol and a 6000 Damolecular weight glycerine initiated polyoxypropylene triol, alsoDMC.glyme catalyzed. Both the latter polyols had unsaturations of c.a.0.014-0.015 meq/g. The polyols used in Example 8 were similar to thoseof Comparative Example I, but both DMC.TBA catalyzed, with unsaturationsof 0.005 meq/g and 0.007 meq/g, respectively. Both polyols wereessentially monodisperse.

The microcellular shoe sole formulations used are presented in Table 6,below, in parts by weight.

                  TABLE 6                                                         ______________________________________                                        COMPONENT          AMOUNT                                                     ______________________________________                                        Prepolymer diol    67.9                                                       Prepolymer triol   67.9                                                       Polymer Polyol.sup.1                                                                             14.83                                                      Water              0.61                                                       Niax ® Al Catalyst                                                                           0.1                                                        UL-1 Catalyst      0.02                                                       Tegostab B4113 Surfactant                                                                        0.1                                                        ______________________________________                                         .sup.1 A polymer polyol prepared from a glycerine initiated                   polyoxypropylene triol conventionally base catalyzed, containing 43 weigh     percent of a styrene/acrylonitrile polymer dispersion and having a            hydroxyl number of 20.2.                                                 

The properties of the microcellular elastomers are presented in Table 7.

                  TABLE 7                                                         ______________________________________                                        EXAMPLE:     H          I          8                                          POLYOL       Conventional                                                                             DMC-Glyme  DMC--TDA                                   IN PREPOLYMERS:                                                                            Base Catalyzed                                                                           Catalyzed  Catalyzed                                  ______________________________________                                        Density, g/cm.sup.3                                                                        0.36       0.38       0.37                                       Hardness, Shore A                                                                          29         34         35                                         Resiliency, %                                                                              39         46         48                                         Tear, Die C, lb/in. (N/m)                                                                  44 (7705)  49 (8581)  52 (9106)                                  Compression Set, %                                                                         18.2       8.8        5.8                                        ______________________________________                                    

The results presented in Table 7 illustrate that despite the analyticalsimilarity of DMC.glyme and DMC.TBA catalyzed polyols, the essentiallymonodisperse, ultra-low unsaturation polyols produce microcellularelastomers with enhanced properties. The increase in resiliency and tearstrength are both notable. However, the decrease in compression set isespecially noteworthy. Compression set is one of the more importantcharacteristics in microcellular elastomer shoe sole formulations. Thelow compression set obtained with ultra-low unsaturation polyols is 35%lower than even the DMC.glyme catalyzed polyol elastomers. Further, thislow compression set has been found to be repeatable, and is expected tobe lower still when polymer polyols employing ultra-low unsaturationbase (carrier) polyols become available.

Examples 9-11 and Comparative Examples J-L

In one-shot shoe sole formulations which do not employ prepolymers or doso only in minor amounts, the reactivity of the polyols must beincreased in order to achieve satisfactory demold times, and thuspolyoxyethylene capped polyorypropylene polyols are utilized. Threeone-shot, ultra-low density microcellular shoe sole formulations,1,4-butanediol extended, and containing various amounts of Polyol A, amonodisperse, ultra-low unsaturation 4000 Da molecular weightpolyoxypropylene diol with a 14.6 weight percent polyoxyethylene cap, ahydroxyl number of 28.3, and an unsaturation of only 0.005 meq/g, andPolyol B, a monodisperse, ultra-low unsaturation 6000 Da molecularweight glycerine initiated polyoxypropylene triol containing 14.7 weightpercent polyoxyethylene as a cap, a hydroxyl number of 28.5 and anunsaturation of only 0.006 meq/g, were prepared, and their physicalproperties measured. For comparison purposes, similar formulations usingconventionally catalyzed polyols C and D were used. Polyol C is a 4000Da diol having a hydroxyl number of 28.5, a 20% weight percentoxyethylene cap, and an unsaturation of 0.06 meg/g, while Polyol D is a6000 Da triol with a hydroxyl number of 28, a 15 weight percentoxyethylene cap and an unsaturation of 0.06 meq/g. Polyols C and D areavailable from the ARCO Chemical Company as ARCOL® 1025 and E785polyols, respectively. The formulations and physical properties arepresented in Table 8.

                  TABLE 8                                                         ______________________________________                                        EXAMPLE  9       J       10    K     11    L                                  ______________________________________                                        4,4-'MDI 33.6    33.6    33.6  33.6  33.6  33.6                               Polyol A 29.4            47.0        47.0                                     Polyol B 29.4            11.8        11.8                                     Polyol C         29.4          47.0        47.0                               Polyol D         29.4          11.8        11.8                               1,4-butanediol                                                                         5.9     5.9     5.9   5.9   5.9   5.9                                Water    0.60    0.60    0.60  0.60  0.60  0.60                               DABCO ®                                                                            0.196   0.196   0.196 0.196 0.196 0.196                              33LV                                                                          POLYCAT  0.1     0.1     0.1   0.1   0.1   0.1                                SA102                                                                         NIAX ® A-1                                                                         0.1     0.1     0.1   0.1   0.1   0.1                                UL-1     0.004   0.004   0.004 0.004 0.004 0.004                              Surfactant                                                                             Y10515  Y10515  Y10515                                                                              Y10515                                                                              Y10788                                                                              Y10788                             Density, g/cm.sup.3                                                                    0.21    0.22    0.22  0.22  0.22  0.22                               Hardness,                                                                              55      42      50    40    46    41                                 Asker C                                                                       Shrinkage, %                                                                           0.5     4.9     0     14.2  18.5  30.7                               ______________________________________                                    

Examples 9-11 and Comparative Examples J-L show that the one-shotmicrocellular elastomers prepared using polyol blends having ultra-lowunsaturation less than 0.010 meq/g surprisingly exhibit considerablyreduced shrinkage as compared to otherwise identical formulationsemploying a blend of conventionally catalyzed polyols. Reduced shrinkageis a property of paramount importance in microcellular elastomers,particularly those for use in shoe soles (i.e., midsoles).

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

What is claimed is:
 1. A one-shot polyurethane microcellular elastomerprepared by the reaction of a di- or polyisocyanate in the presence offrom about 0.1 to about 1.0 weight percent water with an isocyanatereactive component comprising a polyol component, wherein said polyolcomponent comprises one or more polyoxypropylene polyols, saidpolyoxyalkylene polyols comprising in excess of 50 weight percent, basedon the total weight of said one or more polyoxypropylene polyols, of oneor more polyoxypropylene diols having an unsaturation of less than 0.010meq/g, said polyol component having an average unsaturation of less than0.010 meq/g, and optionally one or more polymer polyols.
 2. Themicrocellular elastomer of claim 1 wherein said one or morepolyoxypropylene diols together have a polydispersity of about 1.4 orgreater.
 3. The microcellular elastomer of claim 1 wherein at least oneof said one or more polyoxypropylene polyols is apolyoxypropylene/polyoxyethylene copolymer polyol.
 4. The elastomer ofclaim 3 wherein at least a portion of said polyoxyethylene moieties arepresent as a cap in amounts of from about 5 weight percent to about 20weight percent based on the weight of thepolyoxypropylene/polyoxyethylene polyol.
 5. The microcellular elastomerof claim 1 wherein said elastomer has reduced compression set ascompared to an elastomer prepared from an identical formulation buthaving a polyol component having an average unsaturation of 0.010 meq/gor higher.
 6. A shoe sole comprising the microcellular elastomer ofclaim
 5. 7. The shoe sole of claim 6 wherein said microcellularelastomer comprises a midsole.
 8. The microcellular elastomer of claim 1wherein said elastomer has reduced shrinkage as compared to an elastomerprepared from an identical formulation but having a polyol componenthaving an average unsaturation of 0.010 meq/g or higher.
 9. A shoe solecomprising the microcellular elastomer of claim
 8. 10. The shoe sole ofclaim 9 wherein said microcellular elastomer comprises a midsole.
 11. Amicrocellular polyurethane elastomer which comprises the reactionproduct of:(a) a prepolymer prepared by the reaction of an excess of di-or polyisocyanate with a monodisperse polyoxypropylene diol having amolecular weight of from 1000 Da to about 20,000 Da, a polydispersity ofabout 1.20 or less, and an unsaturation of less than about 0.008 meq/g;with (b) a glycol chain extender;wherein the microcellular polyurethaneelastomer exhibits a demold time of 60 minutes or less, and has adensity of about 0.80 g/cm³ or less.
 12. The microcellular elastomer ofclaim 11 wherein said elastomer has reduced compression set as comparedto an elastomer prepared from an identical formulation but having apolyol component having an average unsaturation of 0.010 meq/g orhigher.
 13. A shoe sole comprising the microcellular elastomer of claim12.
 14. The shoe sole of claim 13 wherein said microcellular elastomercomprises a midsole.
 15. The microcellular elastomer of claim 11 whereinsaid elastomer has reduced shrinkage as compared to an elastomerprepared from an identical formulation but having a polyol componenthaving an average unsaturation of 0.010 meq/g or higher.
 16. A shoe solecomprising the microcellular elastomer of claim
 15. 17. The shoe sole ofclaim 16 wherein said microcellular elastomer comprises a midsole.